"In the second half, this young team showed mental strength," he added. "The players from the bench made the difference."

After clinically finishing Eden Hazard's 80th-minute pass, Mertens admitted that while he was disappointed to miss out on a starting role, scoring the winning goal was the perfect reward.

"That is up to the coach and have to accept it, even though it was tough for me," he said. "Eventually I got the goal and I am happy with that."

Kevin De Bruyne -- who played an influential role in both of Belgium's goals -- echoed his coach's assertions over Algeria's strength, stating that his team must not allow the pre-tournament hype to distract them.

"The first half was very difficult," he said. "Algeria played with good organisation. It was a very good team performance in the second half.

"I know there a lot of expectations. For me, we have to take it game-by-game. Every game is different.

"I just want to prepare for Russia. We don't have to look to South Korea and the next round. We can't think too much ahead."